Process for the production of magnesium chlorid.



' UNITED STATES PATENT onnrcn.

JAMES C. GRAVES AND ARTHUR E. SCHAEFER, OF SAGINAW WEST SIDE, MICHIGAN.

PROCESS FOR THE PRODUCTION OF MAGNESIUM CHLORID.

No Drawing.

tional crystallization.

A solution to which our process is appllcable may be a naturalbrmecontaining calcium and magneslum chlorids, with or without sodiumchlorid, or a bittern produced from a natural brine by any commercialprocess and which contains these chlorids. Brines and bitterns vary inthe degree of their concentration and in the proportionate amounts ofchlorids held in solution, but for convenience of description we willhereinafter describe our process as applied to a natural brine, such asthose occurring in Michigan, Ohio and West Virginia. In these brines theamount of calcium chlorid held in solution is usually about two andone-half times as much as the magnesium chlorid. If the totala'nhydrouschlorids of calcium and magnesium be represented by 100, theproportionate anhydrous magnesium chlorid will usually range from 26 to30 parts, and, for. convenience of subsequent description, the calciumand magnesium chlorids in solution will be referred to by theiranhydrous pro-portions Without respect to the concentration of thesolution.

In carrying out our process we first boil the original brine to acertain concentration, and then cool to a certain temperature to causethe formation of crystals which are higher in ma nesium chlorid than theoriginal brine. The mother liquor is then drawn oil and the crystalsdissolved. The new solution is then boiled to a lower concentration andcooled to form a second crop of crystals still higher in magnesiumchlorid. The mother liquor is drawn off and the new crystals dissolved.These steps are repeated a desirable number of times to obtain a desiredpurity of magnesium chlorid. In each step after the first, the motherliquor when drawn off is sent back to the step preceding Specificationof Letters Patent.

Patented Mar. 10,1914.

Application filed June 15, 1912. Serial No. 703,841.

to be mixed with the solution there being concentrated. Thus, if theprocess be contlnuous 1n five steps through five concentrating pans, thedissolved crystals will move .step by step from the earlier to the laterpans of the series while the mother liquor 3 will move in the reversedirection from the later toward the earlier pans. When sodium chlorid ispresent in the original brine or bittern it may be removed by apreliminary step. This preliminary step consists of concentrating thebrine to about 45 Baum and cooling to about 100 Fahrenheit. The crystalsformed will include practicallyall of the sodium chlorid and smallquantities of calcium and magnesium chlorids. These crystals may besavedor run to the sewer, or the calcium and magnesium chlorids may berecovered by washing with water. In what is to follow We will assumethat this preliminary step is unnecessary or has already been takenl Forthe purpose of making clear the principles upon which our process isfounded we will make certain preliminary statements of matters whichinfluence the manner of carrying out the process.

(a) After concentration by evaporating and upon cooling the brine,magnesium chlorid crystallizes more-rapidly than ealcium chlorid as longas the cooling process is not carried below a certain criticaltemperature, but this difference in rate of-crystallization depends uponthe relative proportions of magnesium and calcium chloride in thesolution and upon the concentration to which the solution is boiled.Below the critical temperature, calcium chlorid crystallizes morerapidly than magnesium chlorid. Hence, cooling is stopped before thecritical temperature is reached.

('0) In any solution, the higher the concentration to which it is boiledthe greater is the yield of crystals and the higher is the proportion ofcalcium chlorid in them. Also, a saturated solution of magnesium chloridis of much lower gravity than a saturated solution of calcium chlorid,hence, the degree of concentration in, the successive steps of theprocess decreases as the solutions are richer in magnesium chlorid andpoorer in calcium chlorid.

In the statement (a) reference is made to a critical temperature abovewhich magnesium chlorid crystallizes more rapidly than calcium chlorid,and below which calcium chlorid crystallizes more rapidly than magnesiumchlorid.

ture varies with the ratio of calclum and 5, magnesium to each otherinthe solution. In a solution containing 71 parts of calcium chlorid to29 parts of magnesium chlorid, the critical temperature is about 7 7Fahrenheit, when the solution contains 60 parts 1 of calcium chlorid to40 parts of magnesium chlorid, the critical temperature is about 58Fahrenheit; with a solution having 40 parts of calcium chlorid to 60parts of magnesium chlorid, the critical temperature is about 40 1Fahrenheit; and in a solution containing 24 parts of calcium chlorid to7 6 parts of magnesium chlorid, the critical temperature is below 32Fahrenheit. With these points 7 determined it is easy toplot a diagramwhich will give the critical temperatures at other relative proportionsof calcium and magnesium to each other. As the process consists in theelimination of calcium chlorid so as to leave a nearly pure magnesiumchlorid and as the quantity of magnesium chlorid in each crop ofcrystals, increases by each cooling after concentration, it is desirablethat the cooling process be-carried near to but not below the criticalpoint. By cooling so the solution to near the critical point, say towithin fire or ten degrees of it, the process may be carried out in twoor three steps, depending upon the purity "desired irr the final productof magnesium chlorid. For com- 35 mercial reasons however, it isadvantageous not to'cool so near to the critical point and to use moresteps in producing the final product. In what follows will be given thedetails of a continuous five-step process- 40 which we have found to besatisfactory in ordinary commercial operations.

Assuming an original brine or mother liquor having 71 parts of calciumchlorid and 29 parts of magnesium chlorid, and to have been previouslyfreed from sodium chlorid, this'solution is boiled in pan No. 1

to about 457 Baum, as measured in the boiling solution, and cooled to100 Fahrenheit.

The crystals formed will consist of about 60 parts calcium chlorid and40 parts magnesium chlorid. The mother liquor left after thecrystallization will contain about 86 parts of calciumchlorid and l4parts of magnesium chlorid, and is drawn as and used for other purposes..The crystals formed in pan No. 1 are dissolvedto form a new solutioncontaining parts of calcium chlorid to 40 parts of magnesium chloridwhich is sent to pan No. 2. This solution is 60 boiled to 43 Baum andcooled to Fahrenheit. The new crop of crystals formed consist of about40 parts of calcium chlorid and 60 parts of magnesiumchlorid; The motherliquor, from which this crop of B5 crystals is obtained, contains about71 parts This critical temperav concentrated in that pan.

,viously described.

: s ium chlorid and is pumped back into pan No. l to form part of thesolution to be next The crystals formed in pan No. 2 are dissolved andsent to pan No. 3. This solution is boiled to 39 Baum and cooled to 70Fahrenheit. The resulting crystals in pan No. 3 consist of about 24parts of calcium chlorid and 7 6 parts of magnesium chlorid, and themother liquor contains about 52 Y parts calcium chlorid to .48 part ofmagnesium chlorid. This mother liquor is pumped back to pan No. 2 andthere mixed with the dissolved crystals coming from pan No. 1. Thecrystals formed in pan No. 3 are dissolved and sent to pan No. 4 wherethe solution is boiled to 36 Baum and cooled to 70 Fahrenheit.

'7 0 Fahrenheit. The resulting crystals consist of about 4 parts ofcalcium chlorid and 96 parts of magnesiumchlo-rid, while the motherliquor contains about 18 parts of calcium chlorid and 82 parts ofmagnesium chlorid and is pumped back into pan No. 4. The crystals formedin-pan No.'5 are dissolved and sent to a concentrator where they areconcentrated to dry fused crystals ready for market; If more than 96 percent. of purity is desired, the process may be carried one or more stepsfurther before fusing.

When it is desired to remove by some other means the calcium chloridremaining after the last step in a process having any number of stepssuch as those described,- We

add to a solution of'the dissolyed crystallized product a solublesulfate, preferably magnesium sulfate, whereupon the calcium chlorid isremoved by'the formation of an insoluble calcium sulfate. The chemicalformula for. this is:. t

. CaCl +MgSO MgCl +CaSO This process of removing the calcium chlorid bychemical reaction and the precipitation of an insoluble calcium sulfatemay be applied at any time, but we find it more economical to apply itto solutions flowfin calcium chlorid,'-i. 6., after several steps havebeen taken in the crystallizing process pre- Instead of applyingmagnesium sulfate directly We may accomplish the same result by addingto the solution an excess of magnesium hydrate in suspension, and thenadding a sufficient quantity of sulfuric acid.

This dissolves the magnesium hydrate with the formation of magnesiumsulfate, which in turn precipitates the insoluble calcium sulfate asbefore described. The excess of magnesium hydrate serves to preventcorrosive action by the sulfuric acid on the containers employed andalso to remove by presolution has been cooled to the critical temwhichcalcium chlorid crysperaturc below rapldly than magnesium tallizcs morechlorid.

2. The process of separating magnesium chlorid by successivecrystallizations from solutions containing calcium and magnesiumchlorids which consist in boiling each successive solution to a lessdegree of concentration and in arresting each crystalllzmg step beforethe solution has been cooled to the critical temperature. I

3.-The process of separating magnesium chlorid from solutionscontainingcalcium and magnesium chlorids by successlve fractionalcrystallizations each of which occurs in a different pan, which processconsists n successively moving and re-dissolving n water thecrystallized parts of the solutions step by step from the earlier to thelater pans of the series of pans, and in moving the mother liquors inthe reverse direction from the later to the earlier pans.

4. The process of separating calcium chlorid and magnesium chloridindividually from solutions containing both of them which consists ineffecting partial crystallization of these salts in each pan of a seriesof pans, in arresting each crystallization before the solution fromwhich it is taking place has been cooled to the critical temperature, inmoving theuncrystalhzed portion of each solution from pan to pan 1n onedirection. and in re-dissolving in water each crop of crystals andmoving the new solutions from pan to pan 1n the opposite (11 rcction.

The process of separating calcium chlorid and magnesium chloridprogressively by partial crystallizatio-ns and re-dissolvmgs in Water ina series of pans from solutions containing bot-h salts which consists inconcentrating the solutions in the different pans to successively lowerdegrees in thesuccessive rid and magnesium chlori pans, in transferringthe mother liquor from each partial crystallization to the pan withinwhich the next higher degree of concentration occurs, and intransferring dissolved crystals from the pan within which they areformed to the pan within which the next lower degree of concentrationoccurs.

6. The process of separatin calcium chloindividually from solutionscontaining both by a series of successive partial crystallizations in. acorresponding series of pans which consists in concentrating thesolutions in successive pans to successively lower degrees, in arrestingthe formation of crystals in each pan before the solution therein hasbeen cooled to its critical temperature, in moving the mother liquor oflater pans to the next earlier pans, and in moving the dissolvedcrystals of earlier pans to the next later pans.

7. The process of separating magnesium chlorid from a solutioncontaining both magnesium and calcium chlorids which consists insuccessively concentrating and cooling the solution to form crystals, inarresting the formation of crystals before calcium chlorid has-begun tocrystallize as rapidly as magnesium chlorid, in re-dissolving thecrystals so formed, and eventually separating the residue of calciumchlorid by adding a soluble sulfate to the new solution to form withsaid calcium chlorid an insoluble precipitate and separating that fromthe solution.

8. The process of separating magnesium chlorid from a solutioncontaining both magnesium and calcium chlorids which consists inremoving the principal part of the magnesium chlorid and some of thecalcium chlorid by crystallization, in re-dissolving the crystals toform a new solution containing a greater relative proportion ofmagnesium chlorid, and in removing the residue of calcium chlorid byaddin to the new solution magnesium hydrate 1n suspension and sulfuricacid and removing the precipitate so produced.

9. The improved process of separating magnesium chlorid from a solutioncontaining that and calcium chlorid, which consists in bothconcentrating and cooling moderately to a point above a critical pointat which the rate of crystallization reverses and the calcium chloridcrystallizes out faster than the magnesium chlorid, then effecting thecrystallization and thereby secur ing a roduct proportionately higher inmagnesium chlorid than existed in the solution, re-dissolving thecrystals so secured in water, again concentrating and cooling to a newpoint above, but approaching, a new critical point at which this newconcentrated solution would reverse its rate of crystallization,effecting the crystallization, and so repeating these series of stepsuntil magnesium chlorid of the desired purity is obtained '10. Theimproved process of separating magnesium chlorid from a solutioncontaining that salt and calcium chlorid, which consists in bothconcentrating and cooling the solution moderately to a point above acritical point at which the rateof crystallization reverses and thecalcium chlorid crystallizes out faster than the magnesium chlorid, theneffecting the crystallization and thereby securing a productproportionately higher in magnesium chlorid than existed in thesolution, recovering and re-dissolving the crystallized product sosecured in Water, again concentrating and cooling to a new point above,but approaching, a new critical point at which this new concentratedsolution would reverse its rate of crystallization, effecting thecrystallization and thus securing a product proportionately higher inmagnesium .chlorid than existed in the solution y from which thisproduct is secured, returning the mother liquor from this step to thesolution of a next preceding similar step, redissolving the crystallizedproduct last secured and again repeating the steps of concentration,cooling and crystallizing, and so repeating until the product secured isof deslred purity, the mother liquor of each cryssubstances, held in ahydrous solution,

which "consists in coolin such solution in concentrated form to effectcrystallization, arresting the crystallizing step when, or'before, thesolution has been cooled to the critical temperature below which thesubstance being separated out ceases to crystallize more rapidly thanthe other contained substance or substances, removing the thus formedcrop of crystals from that solutionand re-dissolving said crystals inwater, then again cooling a concentrated solution of said crystals toeffect crystallization and arresting this crystallizing step when, orbefore, the solution has been cooled to the critical temperature belowwhich the substance being separated out ceases to crystallize morerapidly than the other contained substance or substances and sorepeating un til a desired degree of purity has been attained.

JAMES C. GRAVES. ARTHUR E. SC-HAEFER. Witnesses W. W. SMITH, G. C.CAs'rWoon,

